Question

Two coherent sources produce waves of different intensities which interfere. After interference, the ratio of the maximum intensity to the minimum intensity is 16. The intensity of the waves are in the ratio:

(1) 4 : 1

(2) 25 : 9

(3) 16 : 9

(4) 5 : 3

Answer 1

Ans: (2) 25 : 9

Sol: ${I_{max}\over I_{min}}=16$  

$\implies{A_{max}\over A_{min}}=4$

$\implies{A_1+A_2\over A_1-A_2}={4\over1}$

Using componendo & dividendo.

${A_1\over A_2}={5\over3}\implies{I_1\over I_2}=\left({5\over3}\right)^2={25\over9}$